1. Field of the Disclosure
The present invention relates to an electrophoretic display device, and more particularly, to an electrophoretic display device to enhance both productivity and reliability with a reduced production cost, and a method for manufacturing the same.
2. Discussion of the Related Art
In general, an electrophoretic display device refers to a device capable of displaying images using electrophoresis wherein colored charge particles are moved by an electric field applied from the outside. Here, ‘electrophoresis’ means a phenomenon wherein charged particles are moved in electrophoretic dispersion liquid (electrophoretic ink) by coulomb forces when an electric field is applied to the electrophoretic dispersion liquid having the charged particles dispersed therein.
An electrophoretic display device using electrophoresis has a bistability that allows original images to be displayed for a relatively long time even if an applied voltage is removed. In other words, the electrophoretic display device can maintain a specific screen for a relatively long time without voltages being continuously applied thereto. As a result, the electrophoretic display device may be applied to e-books, which do not require quick changes of screens.
Moreover, an electrophoretic display device has no dependence on viewing angle and can provide images that are comfortable to eyes and remarkably similar to paper, unlike a liquid crystal display device. As a result, demands for the electrophoretic display devices have been increasing because the electrophoretic display devices are flexible, have low power consumption, and are eco-friendly.
Such an electrophoretic display device may be categorized, based on an electrophoretic layer (or film) structure, as a microcapsule type or a microcup type.
FIG. 1 is a sectional view illustrating a structure of a microcapsule type electrophoretic display device according to a related art. With reference to FIG. 1, a microcapsule type electrophoretic display device includes lower and upper substrates 10 and 20 bonded to each other with an electrophoretic film 30 disposed between the lower substrate 10 and the upper substrate 20.
The electrophoretic film 30 includes a first adhesive layer 34 formed of a transparent material, a second adhesive layer 36, a common electrode 38 formed of a transparent conductive material between the first and second adhesive layers 34 and 36, and a plurality of microcapsules having charged particles and electrophoretic dispersion liquid. Although not shown in FIG. 1, the lower substrate 10 includes a plurality of pixel electrodes opposed to the common electrode 38 and a plurality of thin film transistors (TFT) configured as switching devices to apply voltages to the plurality of the pixel electrodes.
The microcapsule 32 includes dielectric solvent, positive (+) charged particles and negative (−) charged particles. The charged particles provided in the microcapsule are moved within the dielectric solvent to present an image.
According to the electrophoretic display device of FIG. 1, the upper substrate 20, the lower substrate 10 and the laminated electrophoretic film 30 are each manufactured. After that, the electrophoretic film 30 is disposed between the lower substrate 10 and the upper substrate 20.
Here, the electrophoretic film 30 is attached to the upper substrate 20 by the second adhesive layer 36, and a release film is kept attached to the first adhesive layer 34. Just before it is laminated on the lower substrate 34, the release film is eliminated. After that, the electrophoretic film 30 is attached to the lower substrate 10 by the first adhesive layer 34.
As described above, the manufacture process of the electrophoretic display device is quite complicated because the lower substrate 10, the upper substrate 10 and the electrophoretic film 30 have to be manufactured separately. As a result, the manufacture of the electrophoretic display device will require much time and productivity might deteriorate disadvantageously. Also, the electrophoretic film 30 additionally has to be manufactured and production cost might be disadvantageously increased.
FIG. 2 is a sectional view illustrating a structure of a microcup type electrophoretic display device according to the related art. With reference to FIG. 2, a microcup type electrophoretic display device includes an upper substrate 40, a lower substrate 50 and an electrophoretic layer internalized on the lower substrate 50.
The upper substrate 40 includes a base substrate 42 (or a base film) formed of a transparent material and a common electrode 44 formed of a transparent conductive material, for example, Indium Tin Oxide (ITO) or Indium Zinc Oxide (IZO).
The lower substrate 50 includes a base substrate 52 formed of a transparent or opaque material and a plurality of pixel electrodes 54 provided on the base substrate 52, in opposite to the common electrode 44. Here, a plurality of thin film transistors (TFT, not shown) may be formed on the base substrate 52 as switching devices to apply voltages to the plurality of the pixel electrodes 54.
The electrophoretic layer includes partition walls 56 to define sub-pixels formed on the lower substrate 50 to display images and electrophoretic dispersion liquid (or electrophoretic ink) 62 injected into the sub-pixels. Here, the electrophoretic dispersion liquid 62 includes dielectric solvent and a plurality of charged particles 64. The charged particles 64 are moved within the dielectric solvent along an electric field formed by the common electrode 44 and the pixel electrodes 54.
According to the microcup type electrophoretic display device having the above configuration, the electrophoretic dispersion liquid 62 is injected into the sub-pixels defined by the partition walls 56 formed on the lower substrate 50. In other words, the electroporetic dispersion liquid 62 is internalized on the lower substrate 50.
Here, when the partition walls 56 are formed of an inorganic material, failure of full injection of the electrophoretic dispersion liquid and vapor generation might occur in the filling process of the electrophoretic dispersion liquid 62 as shown in FIG. 3.
The electrophoretic display device has sealant in an outer area of a display region formed on the lower substrate 50 and the sealant is used to bond the upper substrate 40 with the lower substrate 50. A guide configured to prevent overflow of sealant to inner and outer areas of the sealant coated region is not formed.
As a result, the sealant used to bond the upper and lower substrates 40 and 50 with each other might overflow to an inside and an outside of a display panel as shown in FIG. 4, thereby resulting in operational errors of the display panel. If the sealant overflows to the inside and outside of the display panel, the bonding process between the upper and lower substrates 40 and 50 might not be performed smoothly and properly.
Furthermore, the sealant overflow causes incomplete closure of the display panel with respect to the outside and the electrophoretic display device happens to be contaminated by external air and water elements disadvantageously. As a result, an error generated by overflowing of sealant used to bond the upper and lower substrates to each other might deteriorate productivity and reliability of the electrophoretic display device.